Erythromycins are antibiotics clinically widely used as agents for treating infectious diseases caused by Gram-positive bacteria, some Gram-negative bacteria, mycoplasmas, etc. Many erythromycin derivatives have been prepared for the improvement of biological and/or pharmaceutical properties of erythromycins. Certain ketone forms at the 3-position of 5-O-desosaminylerythronolide A have been described in Antimicrobial Agents and Chemotherapy, vol. 6, No. 4, page 479 (1974) and Journal of Medicinal Chemistry, vol. 17, No. 9, page 953 (1974), but generally they have extremely weak antibacterial activity. An object of the present invention is to provide novel antibiotics having a strong antibacterial activity.